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VESTIBULAR SCHWANNOMA
This fact sheet is intended to give a possible explanation for symptoms you might
experience as a result of having vestibular Schwannomas (formerly called acoustic
neuroma). This information is not intended to replace medical advice from your
specialist. The symptoms discussed here will vary in each person and are not typical of
all vestibular Schwannoma patients. Each case should be individually evaluated by a
doctor who is familiar with your symptoms. In Nf2 other benign tumours in the brain or
on the spine may cause different symptoms.
Understanding the brain and nervous system
The nervous system is a remarkable structure with specific functions localised to
different regions. An understanding of the anatomy and function of the brain and its
cranial nerves can provide an insight into the symptoms that a vestibular Schwannoma
might cause. The information here can also explain the physical changes some patients
experience after the removal of a tumour.
A large portion of the brain is composed of the right and left cerebral hemispheres
that are interconnected through a central structure called the corpus callosum. The
right cerebral hemisphere controls the left side of the body and vice versa.
Each cerebral hemisphere is divided into four lobes: frontal, temporal, parietal, and
occipital. (It is not possible here to discuss all their functions.)
In general terms, much of the frontal lobes are concerned with personality and
emotions; the posterior (back) portion of the frontal and parietal areas are related to
movement and sensation. The occipital lobes are concerned with visual perception. The
temporal lobes are also concerned with many other functions, including threedimensional and spatial perception, memory, and auditory function. For most people,
the ability to speak and understand speech is located in the left cerebral hemisphere
(in parts of the frontal, parietal, and temporal regions).
At the base of the cerebral hemispheres, is an area called the hypothalamus,
connected by a short stalk to the pituitary gland. These structures are concerned
with hormonal control of the body.
Deep inside the cerebral hemispheres there are central controlling and connecting
structures called the basal ganglia, thalamus, and mid-brain. The mid-brain
merges into the brainstem at the back of the base of the skull until it leaves the head,
through an opening called the foramen magnum, to become part of the spinal cord.
All of the connections from the brain to the rest of the body go through the brain stem.
On each side of the brain stem are the right and left cerebellar hemispheres. These
help control co-ordination (the right hemisphere controls the right side of the body)
and the ability to walk.
The brain is bathed in a watery fluid called cerebrospinal fluid which is continually
being formed and reabsorbed. In addition to flowing over the surface, the fluid
circulates in a system of spaces in the brain called ventricles. The brain is supplied by
an extensive network of arterial blood vessels, and blood is drained by a complex
system of veins.
Adapted with kind permission from “A Glimpse of the Brain” a publication of the Acoustic Neuroma Association, USA 200
The Cranial Nerves
In the middle of the base of the brain, beginning behind the bridge of the nose and
extending to the junction of the head and neck, are a paired series of 12 cranial
nerves. These cranial nerves carry impulses from the senses to the appropriate brain
centre, and instructions from the brain centre to other structures (such as muscles
and glands). Historically, these cranial nerves are designated with Roman numerals.
I.
Olfactory — carries sensation from the nose to the brain.
II.
Optic — carries visual impulses from the retina to the brain.
III.
Oculomotor — supplies four of the six muscles that move the eye, and the
muscle that elevates the eyelid.
IV.
Trochlear — supplies one muscle that moves the eye.
V.
Trigeminal — carries sensation from the inside of the mouth, teeth, and front
of the tongue, and skin of the face. It also supplies the muscles of the jaw.
VI.
Abducens — supplies one muscle that moves the eye.
VII.
Facial — supplies the muscles that move the face and the lacrimal and
salivary glands and carries taste sensation from the front of the tongue.
VIII. Auditory — consists of two parts: the cochlear nerve which carries hearing
and the vestibular nerve which transmits impulses from the semicircular canals
which affect balance.
IX.
Glossophyaryngeal — supplies the parotid gland and carries taste sensation
from the back third of the tongue.
X.
Vagus — supplies muscles of the vocal cord and those involved with
swallowing. It gives movement to smooth muscles and affects the secretory
glands in the respiratory and gastrointestinal tracts; is involved with control of
the function of the heart.
XI.
Accessory — supplies muscles that elevate the shoulder.
XII.
Hypoglossal — supplies muscles which move the tongue.
Symptoms
The middle and inner ear structures are located within a bone that forms part of the
base of the skull that extends from the ear toward the centre of the head. An
opening in this bone, called the internal auditory meatus, leads to the internal
auditory canal, which contains the auditory, vestibular and facial nerves. The
vestibular Schwannoma starts near this opening and grows into the canal. Pressure
can cause it to enlarge and it can also extend into the cranial cavity.
The tumour originates in the Schwann cells that form the sheath around the
vestibular part of the eighth cranial nerve. As it grows, it interferes with the function
of the vestibular and cochlear nerves. When the tumour becomes larger, it starts to
compress the brain stem and fifth cranial nerve, the trigeminal nerve.
A very large tumour may involve cranial nerves IV to X and markedly compress the
brain stem and cerebellum. Cranial nerves I, II, III, and XII are usually not involved
with the tumour. The eleventh cranial nerve may rarely be involved with large
tumours. Functions of the cerebral hemispheres are affected only in the rare
circumstances when hydrocephalus (enlargement of the ventricles containing the
cerebrospinal fluid) occurs due to obstruction of the normal circulation of the fluid.
Auditory Symptoms
The first symptom from the tumour is usually some disturbance in hearing, such as
the inability to hear on the telephone, fullness in the ear, and/or tinnitus. This is
probably due to pressure on the cochlear portion of the eighth nerve. The cochlear
nerve is more sensitive to pressure than most other cranial nerves.
The ability to hear requires an intact nerve and an adequate blood supply to the
inner ear hearing structures. In most patients, the blood supply to the cochlear
nerve and the cells receiving the sound in the ear comes from the internal auditory
artery. This artery originates inside the head and passes through the internal
auditory canal with the nerves, and, therefore, will also be involved with the tumour.
Sudden deterioration or fluctuation in hearing may relate to pressure on this artery.
After an operation to remove the tumour the person is usually deaf in that ear
because the cochlear nerve and/or internal auditory artery are intertwined with the
tumour. It is difficult to save the hearing when the tumour is removed. Occasionally
with a small tumour, it is possible to save these structures and preserve hearing.
Radiation therapy may have an effect on the cochlear nerve or the internal auditory
artery. This effect may be seen over several years following therapy, thus the initial
success with hearing preservation may be lost over time.
Unsteadiness and Vertigo
The tumour starts on the vestibular part of the eighth nerve and in some people,
unsteadiness or vertigo may be early symptoms. These symptoms are usually mild or
intermittent because the nervous system adapts quite well to gradual loss of function
in this nerve. In those with larger tumours, pressure on the cerebellum and/or brain
stem might cause difficulty with balance.
Some people will experience a period of dizziness and difficulty with balance after
removal of the tumour. This can be due to abrupt loss of function in the vestibular
nerve fibres that were still intact and had to be divided to remove the tumour. These
symptoms usually subside over days to weeks. Where there is a large tumour, the
involvement of the cerebellum and brain stem or its blood supply may be the cause
of persisting symptoms. Those who undergo radiosurgical treatment may experience
fewer balance problems immediately after treatment; however, because this
treatment takes some time to have its effect, balance problems may be delayed in
emerging.
Facial weakness / dry eye
Because the auditory nerve and the facial nerve are normally next to each other,
every vestibular Schwannoma will involve the facial nerve. Facial weakness before
treatment is uncommon because the facial nerve is quite resistant to pressure,
although, a few people notice intermittent spasm or difficulty blinking the eye.
Postoperative facial weakness is due to the reaction in the nerve after it has been
separated from the tumour capsule or occasionally divided totally from the nerve. If
there is inability to close the eyelids, a minor procedure might be required to improve
this function. A small percentage of those undergoing radiosurgical treatment also
experience facial weakness post-treatment.
A dry eye is due to the loss of innervation (nerve supply) through this nerve to the
lacrimal gland. Occasionally this portion of the facial nerve “over recovers” and
carries excessive impulses so that too many tears are provided, especially when
chewing. Facial nerve fibres also serve the secretory glands in the nose, so this
function may be affected by either excessive or inadequate secretion.
Facial Numbness
As the tumour becomes larger, there can be pressure on the trigeminal (fifth) cranial
nerve causing numbness of the face and/or numbness of the mouth or tongue. Usually
this symptom subsides with removal of the tumour, but occasionally the numbness is
worse. A serious problem occurs when there is a facial paralysis with inability to close the
eye and sometimes loss of sensation on the cornea. Special ophthalmologic care is
required to protect the cornea.
Facial Pain
This is an uncommon symptom and is due to pressure on the trigeminal nerve. The
description of the pain may be similar to that seen with trigeminal neuralgia with sudden
stabs of severe pain. Fortunately this problem is rare after surgery.
Poor co-ordination in legs or arms
The control of co-ordination in the limbs is located in the cerebellar hemispheres and
adjacent brain stem. In some large tumours, a problem in hand co-ordination might cause
difficulty with some daily activities. The legs may also be affected. Often a program of
physiotherapy is required to aid recovery in the post-treatment period.
Weakness or loss of sensation in extremities
In some people with large tumours, this problem is due to brain stem compression. When
it occurs postoperatively, it is usually due to blocking of the blood supply to the brain
stem. In some large tumours the important arteries in the area supply both the tumour
and the brain stem, and it might be difficult to separate them.
Double vision
Double vision can be due to a loss of function in either the nerves supplying the eye
muscles or the brain stem centres that co-ordinate eye movement. The third cranial
nerve lies above the tumour and is not affected. In large tumours, the fourth cranial
nerve may be involved.
Difficulty Swallowing
Fortunately this is a very rare symptom both before and after treatment. When it does
occur, it is due to involvement of the tenth cranial nerve fibres or blocking of some of the
blood supply to the brain stem.
Headaches
Headaches before having treatment are uncommon. When they do occur, they are usually
associated with a large tumour. Some people complain of aching in or around the ear,
probably from a reflex through the seventh or fifth nerve. When these are present after
treatment, a CT scan or MRI is done to look for a specific cause, such as hydrocephalus.
In most cases no special cause is found. Symptomatic treatment is given, and usually
there is gradual recovery.
The Neuro Foundation has taken reasonable care to ensure that the information
contained in its publications is accurate. The Neuro Foundation cannot accept
liability for any errors or omissions or for information becoming out of date. The
information provided is not a substitute for getting medical advice from your own
GP or other healthcare professional.
The Neuro Foundation,
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London SW20 0TL
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